Storage lockers are used in a number of environments such as industrial, commercial, military and educational institutions for temporary storage of personal items such as clothing, books, sporting equipment and the like. An example of a knock-down locker is shown by Novales in U.S. Pat. No. 3,360,321. This locker has a top shelf permanently attached to the locker side walls. The shelf has a fixed length and fits into a specific size locker. Boards and plywood panels have been used as auxiliary or additional locker shelves. The panels are made slightly wider than the width of the locker so that they can be wedged against the locker side walls to hold them in a selected vertical position. The wedging of the panels against the side walls distorts and bends the locker side walls and the door frame. In some cases, the door frame is warped so that the locker door cannot be closed. Lockers are normally located in side-by-side locations such as found in schools. When one locker is distorted, the adjacent locker is also distorted. This can cause the locker doors to jam shut or prevent the locker doors from closing. R. R. Peterson in U.S. Pat. No. 4,500,146 discloses a laterally adjustable locker shelf assembly having a plurality of locker shelves mounted on upright legs. Each locker shelf can be laterally expanded to position the locker shelf assembly within a locker. The locker shelf assembly of the invention is an expandable shelf assembly that does not utilize support legs to locate the shelf assembly within a locker.